Not working. It's 2€ and 1€ in Store as well.
All of the reasons you mention are of very little use. The real benefit comes from not having to manually update anything (or hoping the publisher of the software has implemented their own system for automatic updates).
That said, not worth it to me in most cases since software outside Store is usually better, but it's still a valid point.
I'm not sure what you mean? That's why I use Torrex Pro. Very little use to whom?